Are adaptive zones important in macroevolution?

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Many researchers think that most of life's staggering diversity may have arisen by a process known as adaptive radiation. In adaptive radiation, an ancestral population gets an evolutionary windfall - for any of several reasons, it finds itself surrounded by a set of empty niches, and so diversifies both taxonomically and ecologically, resulting in a range of species adapted to different niches. This model assumes that niches in nature really are ordered hierarchically into groups known as adaptive zones; niches in the same adaptive zone are sufficiently similar that, given time, a species adapted to any one of them could colonise and adapt to the others.These adaptive zones are among the longest-standing metaphors in evolutionary biology; since it was proposed in 1944, the idea has shaped thinking about evolutionary 'arms races', where competing species are locked in an ongoing struggle of thrust and counterthrust, as well as about adaptive radiation. If the idea is right, it makes predictions about how ecological communities and groups of closely-related species will evolve. Surprisingly, however, we don't really know how important adaptive zones have been in shaping the pattern of evolution. Progress has been difficult because most groups that everyone agrees are adaptive radiations don't have a good fossil record, because many of these groups can only be studied in one place (frustrating scientists' desire to replicate their findings), and because most places on Earth have changed so much over geological time that climate change is a possible explanation for whatever pattern is seen.We propose to investigate the importance of adaptive zones in shaping large-scale evolutionary patterns by focusing on the group with probably the best fossil record of all - a group of single-celled oceanic microbes called planktonic foraminifera - in two of the world's oldest and most stable ecosystems - the North Pacific and North Atlantic subtropical oceanic gyres. Within each gyre, we will take fossil samples every million years back to 23 million years ago; this is made possible by the many expeditions that have drilled the sea bed and brought back layer upon layer of fossils that had accumulated there. We will estimate how abundant each species was at each time slice, and take detailed measurements of their sizes and shapes.Our data will provide an unprecedentedly rich picture of how the group has evolved in this unusually stable system, so we can test whether predictions from adaptive zones are correct. For example, if each adaptive zone provides a different way of being an evolutionary success, then we should see species' size and shape evolve towards those same successful morphologies time and again; and, if species within an adaptive zone compete, then when one became more abundant through time its competitors should have become rarer. If morphology and abundance produce a consistent picture of what the MPF adaptive zones have been, then they will also provide an objective way of delimiting adaptive zones - something that we currently lack.Our data will also help to develop a better understanding of how size and shape evolve along the branches of the evolutionary 'family tree' that links all species, providing answer to longstanding questions: When does morphology change quickly and when slowly? Do species within an adaptive zone affect each other's evolution - and indeed whether they even survive?Most adaptive radiations don't allow researchers to ask such questions (or, even if they do, they force us to make many untestable assumptions). However, though our results couldn't be obtained for those other systems, our findings will be of interest to the researchers working on them: we may identify important processes that their analyses currently omit. As well as telling us about planktonic foraminifera, this project will help us understand how much of life's diversity may have arisen.